MIT neuroscientists report in Science a circuit that links a sensory decision region with a pathway that evaluates how much the sensory world has just changed. The circuit connects the anterior cingulate cortex (ACC) in the prefrontal cortex with the pulvinar‑like lateral posterior thalamus (LP) in mice, allowing a comparison between what just happened and what is happening now, which then guides whether a decision should be kept or updated.\ \ Mice were trained to play a simple video‑game: dots drifted on a screen, and a subset moved coherently left or right. Each trial varied both the direction and the proportion of coherent dots (e.g., 64% left vs. 16% right), creating a continuum of sensory differences. Two‑photon microscopy recorded LP‑ACC activity while optogenetics briefly boosted LP inputs to ACC. Behavioral analysis showed that after a correct guess, mice tended to repeat the guess when the new cue resembled the previous one and to switch when it differed; after an error, the pattern reversed.\ \ Optogenetic perturbation revealed causality: stimulating left‑hemisphere LP‑ACC inputs reduced right‑ward choices, while right‑hemisphere stimulation increased them, and the magnitude of the bias scaled with the difference between current and prior cues. This demonstrates that the pathway is essential for the comparison process rather than merely carrying sensory information.\ \ Imaging data indicated distinct roles: the pulvinar‑like LP supplies a history‑referenced sensory comparison, whereas the ACC transforms that signal into neural activity that predicts the animal’s final choice. In other words, the thalamic node advises the frontal cortex on the degree of change, enabling the brain to decide whether to stick with the current hypothesis or to revise it.\ \ Beyond basic neuroscience, the work may inform studies of autism, where predictive processing of sensory input is often altered. The project was funded by the NIH, a MURI grant, the Simons Foundation Autism Research Initiative, A*STAR, and the Freedom Together Foundation.\ \ Review